Making rain may seem a bit like alchemy, but the practice has been around since the 1940s, when engineers at General Electric began experimenting with dumping dry ice into clouds from airplanes. Water districts and ski resorts around the West got into the practice in the 1970s, shooting silver iodide into winter clouds from mountain-top cannons.

Silver iodide crystals behave like ice, attracting water droplets to them until they grow big enough to fall to the ground as snow. Cloud seeding advocates say the practice is inexpensive—$10-20 per acre-foot of water created—and can boost snowfall by 10 to 15 percent. They’re also quick to point out there are no documented negative environmental effects of the process.

But it’s hard to separate cloud seeding-induced precipitation from what falls naturally from the sky. A 2010 study by Israeli researchers examining rainfall patterns and cloud seeding over the Sea of Galilee in Northern Israel found that a series of cyclones were responsible for increased rainfall over a six-year period, not cloud seeding. The state of Wyoming is currently spending $11 million on a multi-year study to determine whether the practice works and is cost-effective. Results are expected in 2014.

Still, the science is apparently convincing enough for water districts in Southern California, Nevada and Arizona to pay Upper Colorado River Basin states to seed clouds. Since 2006, Lower Basin states have spent over $800,000 in Colorado and around $500,000 in Utah and Wyoming.

“We're believers down here," Tom Ryan, a resource specialist for the Metropolitan Water District of Southern California who coordinates cloud seeding for the Lower Basin states, told the magazine ColoradoBiz in 2010. "The Lower Basin folks believe it works. We believe that the science is adequate to move forward."

In 2006, the water district of Durango, Colo., became the first in the Upper Basin to receive out-of-state money for cloud seeding. The Met's Ryan approached the town because he heard they had had a dry winter. He’d also heard the district had run out of money for their own cloud seeding projects, and wanted to know if they were interested in a little bit of Lower Basin cash. Durango said yes, and Ryan sent them $45,000. Soon after, Ryan says their snowpack increased from 56 to 76 percent of normal.

Other states and water districts heard about Durango's success and soon called Ryan, asking him to fund their cloud seeding projects. Since then, Lower Basin states have spent more every year on cloud seeding in Wyoming, Utah and Colorado. Although Lower Basin spending on cloud seeding is up 89 percent since 2006, to $425,000 in 2013, expenditures aren’t likely to increase anymore.

“We’re going to hold steady for a while,” Ryan said. “We’re starting to get an idea of which areas are more productive and which are less.”

Part of the reason for the plateau is that Ryan is waiting for the results of the Wyoming study. He said it’s too early to say what the Lower Basin states will do with the results, but they seem interested in seeing additional scientific evidence showing that the process works and is cost-effective before spending further.

Lower Basin states have not funded their own studies to determine how effective the cloud seeding is, Ryan said.

In the mean time, many water experts say conservation is going to go a lot further towards solving the West’s water crisis than shooting silver iodide into clouds over the Wind River Mountains or Grand Mesa.

“It’s a small augmentation tool,” said Joe Busto, who manages Colorado’s cloud-seeding operation for the Colorado Water Conservation Board, “it’s not a cure-all for everything.”

But, he says, “if there’s anywhere to do ground-based cloud seeding and really have it be effective, it’s here.”

More from Water

From a science perspective one has to remember that you can't get something from nothing. What I mean is that even if, and that's a very large if, cloud seeding worked in the Rockies, then who exactly are they stealing that water vapor from? If cloud seeding causes precipitation to fall in the Rockies, then that vapor isn't available to fall where it otherwise would have. It kind of reminds me of the guy in Denver who got charged with stealing water because he had a rain barrel attached to his roof gutter on the premise that he was keeping precipitation from entering the groundwater system that he wasn't entitled to.